The present invention relates to a cylinder injection type internal combustion engine that supplies fuel directly into combustion chambers by fuel injection valves.
JP-A-11-159382 describes a technology directed to a cylinder injection engine (hereafter simply referred to as engine), which comprises fuel injection valves (hereafter simply referred to as injector) for supplying fuel directly into combustion chambers and, when the engine is in an operation zone of low engine speed and low load conditions, injects fuel in compression strokes to stratify and burn air-fuel mixture. The technology is for improving fuel consumption by injecting fuel in plural times during a compression stroke, when the engine is in an operation zone wherein at least either the load or engine speed is relatively high within a stratified combustion region, to thereby extend the stratified operation zone.
JP-A-7-119507 describes a technology of injecting fuel while dividing the same in the uniform combustion (synonymous with homogeneous combustion) region under high load and low engine speed conditions and thus reducing the injection quantity at one time to achieve uniform combustion through effective atomization and diffusion of fuel.
Both the conventional technologies described above employ injectors with long-distance spray penetration and use pistons as guides or hit plugs directly with fuel. Accordingly, the injected fuel deposits on the pistons in the stratified combustion region or deposits on combustion chamber walls after passing through the ignition plugs, and they cannot improve fuel economy or reduce emissions as much as theoretically possible. Besides, even if fuel is divided and injected in plural times at one fuel injection timing, much of the fuel contacts the pistons and the combustion chamber walls due to the character of the system, resulting in insufficient improvement in fuel economy and emission reduction.
Injectors conventionally used in cylinder injection type internal combustion engines are driven by high-voltage generators including capacitors. In case of driving the injector for opening and closing plural times during one injection timing, time for charging the capacitor is required while the valve is closed between injections, and the injection interval cannot be shortened. Accordingly, another problem is that fuel cannot be injected multiple times during one injection timing if the duration of the combustion stroke in a high-speed operation zone is short.
Furthermore, the conventional art described above do not discuss any stratified combustion that takes place in such an engine operation zone wherein a starter is operated. This means that an engine is started with a high air-fuel ratio to avoid combustion failure because a failure in stratified combustion under such conditions will result in several times the normal amount of HC emissions to make it impossible to meet severe European emission regulations.
However, the higher the air-fuel ratio used for starting, the more HC is emitted. Besides, the conventional art described above do not give consideration to the fact that operating the injectors multiple times during one fuel injection timing results in heavy power consumption.